Mechanical joint for use in fiber optic imaging systems

ABSTRACT

An example apparatus includes an optical fiber, an actuator, and a joint mechanically coupling the actuator to the optical fiber. The joint includes a neck extending along an axis. The optical fiber is threaded through an aperture extending along the axis through the neck. The optical fiber is attached to the joint at a surface of the neck facing the axis. The joint also includes a collar extending along the axis. The actuator is mechanically attached to the joint at an inner surface of the collar facing the axis. The joint also includes a flexural element extending radially from the neck to the collar. During operation, the joint couples a force from the actuator to the optical fiber to vary an orientation of a portion of the optical fiber extending from the neck with respect to the axis.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/991,851, filed on May 29, 2018, which claims the benefit of thefiling date of U.S. Provisional Application No. 62/513,082, filed on May31, 2017. The contents of U.S. application Ser. Nos. 62/513,082 and15/991,851 are incorporated herein by reference in their entirety.

TECHNICAL FIELD

This disclosure relates to mechanical joints for use in fiber opticimaging systems, such as fiber scanned display devices.

BACKGROUND

Imaging systems can be used to present visual information to a user. Forexample, an imaging system can include an optical component thatprojects images onto an imaging surface, such that one or more users canview the image. In some cases, imaging systems can be incorporated intoa head-mounted display device to present visual information in a moreimmersive manner. For example, head-mounted displays can be used topresent visual information for virtual reality (VR) or augmented reality(AR) systems.

SUMMARY

Implementations of a mechanical joint for physically coupling anactuator to a waveguide are described herein. One or more of thedescribed implementations can be used in conjunction with fiber opticimaging systems, such as fiber scanned display devices.

Implementation of the mechanical joint can provide various benefits. Forexample, one or more of the mechanical joints described herein enable afiber optic imaging system to operate with a high degree of precision,thereby improving image quality. Further, one or more of the mechanicaljoints described herein can be constructed precisely and consistently,and thus may be suitable for use in variation-specific applications(e.g., in imaging systems that may be highly sensitive to the propertiesof a mechanical joint, such as fiber scanned display devices). Further,mechanical joints can be readily mass produced. Further still, thedesign of mechanical joints can be readily modified and implemented, andthus can be readily used in a variety of different applications. Ingeneral, in an aspect, an apparatus includes an optical fiber, anactuator, and a joint mechanically coupling the actuator to the opticalfiber. The joint includes a neck extending along an axis. The opticalfiber is threaded through an aperture extending along the axis throughthe neck. The optical fiber is attached to the joint at a surface of theneck facing the axis. The joint also includes a collar extending alongthe axis. The actuator is mechanically attached to the joint at an innersurface of the collar facing the axis. The joint also includes aflexural element extending radially from the neck to the collar. Duringoperation, the joint couples a force from the actuator to the opticalfiber to vary an orientation of a portion of the optical fiber extendingfrom the neck with respect to the axis.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the flexural element can include an annularportion extending between the neck and the collar.

In some implementations, the flexural element can include one or morebeams extending between the neck and the collar.

In some implementations, the collar can extend along the axis in adirection away from the neck.

In some implementations, the collar can extend along the axis about aperiphery of the neck.

In some implementations, the joint can be rotationally symmetric aboutthe axis. The joint can have at least four-fold rotational symmetryabout the axis. In some implementations, the joint can have a firststiffness with respect to the axis, a second stiffness with respect to afirst radial direction, and a third stiffness with respect to a secondradial direction orthogonal the first radial direction. The firststiffness can be greater than the second stiffness and the thirdstiffness. The second stiffness and the third stiffness can besubstantially equal.

In some implementations, the joint can include crystalline silicon. Thecrystalline silicon can have a (111) crystal structure.

In some implementations, the joint can include amorphous silicon.

In some implementations, the joint can include one or more layers ofsilicon and one or more layers of electrically insulative material. Theelectrically insulative material can include silicon dioxide.

In some implementations, the outer portion can have a substantiallycircular cross-section. The neck can have an inner diameter less than200 μm. The neck can have an outer diameter less than 300 μm.

In some implementations, the neck can define one or more slots along aperiphery of the neck.

In some implementations, the collar can have a substantially circularcross-section. The collar can have an inner diameter less than 1500 μm.The collar can have an outer diameter less than 2000 μm.

In some implementations, the collar can define one or more slots along aperiphery of the collar.

In some implementations, the apparatus can further include anillumination source in optical communication with the optical fiber. Theillumination source can be configured, during operation, to direct lightinto the optical fiber. The actuator can be configured, duringoperation, to vary the orientation of the portion of the optical fibersuch that a first end of the optical fiber traverses a pre-definedpattern. The optical guide can be configured, during operation, toreceive light from the illumination source, guide the received light toan end of the optical fiber, and emit the received light from the firstend of the optical fiber.

In some implementations, the flexural element can define one or moreslots extending through the flexural element.

In some implementations, the one or more slots can be spirally arrangedabout the axis.

In some implementations, the flexural element can include a gimbalstructure. The gimbal structure can include a ring, a plurality of innerbeams mechanically coupling the neck to the ring, and a plurality ofouter beams mechanically coupling the ring to the collar.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features and advantages willbe apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic diagram of an example fiber scanned displaydevice.

FIG. 1B shows an example deflection of a waveguide tip.

FIG. 1C shows a plot of an example modulation pattern.

FIG. 1D shows an example scan pattern.

FIG. 2A shows a perspective view of an example actuator, an examplewaveguide, and an example mechanical joint.

FIG. 2B shows a cross-sectional view of the components shown in FIG. 2A.

FIG. 3A shows a front perspective view of the example mechanical jointshown in FIGS. 2A and 2B.

FIG. 3B shows a rear perspective view of the example mechanical jointshown in FIGS. 2A and 2B.

FIG. 3C shows a cross-sectional view of the example mechanical jointshown in FIGS. 2A and 2B.

FIG. 3D shows a top view of the example mechanical joint shown in FIGS.2A and 2B.

FIG. 4A shows a rear perspective view of the example mechanical jointshown in FIGS. 2A and 2B.

FIG. 4B shows a top view of the example mechanical joint shown in FIGS.2A and 2B.

FIG. 4C shows a perspective view of the example actuator, the examplewaveguide, and the example mechanical joint shown in FIG. 2A.

FIG. 5A shows a perspective view of another example mechanical joint.

FIG. 5B shows a top view of the mechanical joint shown in FIG. 5A.

FIG. 5C shows a cross-sectional view of the mechanical joint shown inFIG. 5A.

FIG. 6A shows a perspective view of another example mechanical joint.

FIG. 6B shows a top view of the mechanical joint shown in FIG. 6A.

FIG. 6C shows a cross-sectional view of the mechanical joint shown inFIG. 6A.

FIG. 7A shows a perspective view of another example mechanical joint.

FIG. 7B shows a top view of the mechanical joint shown in FIG. 7A.

FIG. 7C shows a cross-sectional view of the mechanical joint shown inFIG. 7A.

FIGS. 8A-8C show an example microfabrication process for producingmechanical joints.

DETAILED DESCRIPTION

In general, a fiber scanned display (FSD) device projects images onto animaging surface by directing a time-modulated light pattern through anoptical fiber while vibrating the optical fiber tip. For instance, a FSDdevice can vibrate an optical fiber using an actuator, such that the tipof the optical fiber travels along or “scans” a predictable predefinedpattern or path (e.g., a spiral). As the tip of the optical fiber scansthe pattern, modulated light is transmitted through the optical fiber,such that light is emitted from the tip of the optical fiber in aspatially-dependent manner. Accordingly, images can be spatially“scanned” onto an imaging surface by continuously vibrating the opticalfiber while transmitting a sequence of light pulses into the opticalfiber.

An example FSD device 100 is shown schematically in FIG. 1A. The FSDdevice 100 includes several radiation sources 102 a-c configured to emitlight (e.g., a red laser, a green laser, and a blue laser,respectively). The radiation sources 102 a-c are optically coupled to afirst waveguide 104 (e.g., a red-green-blue (RGB) combiner), such thatlight emitted by each of the radiation sources is combined. The combinedlight from the first waveguide 104 is relayed by a second waveguide 106(e.g., a single mode optical fiber) optically coupled to the firstwaveguide 104. In turn, the light from the second waveguide 106 isemitted from its tip 108 (e.g., a cantilevered fiber tip).

The emitted light passes through a lens assembly 110 that focuses theemitted light onto an image plane 112. As the light is being emitted,the waveguide tip 108 is scanned along one or more axes by an actuator114 (e.g., a piezoelectric tube actuator), such that the emitted lightis projected according to a scan pattern along the image plane 112(e.g., a spiral). As a result, a scanned image (e.g., a spiral-scannedimage) is formed on the image plane 112.

As shown in FIG. 1B, the waveguide tip 108 can be scanned by imparting aforce onto the waveguide 106 using the actuator 114. The waveguide 106is flexible, causing the waveguide tip 108 to deflect by an angle αrelative to the longitudinal axis 150 of the actuator 114. Operation ofthe actuator 114 can be selectively regulated to deflect the waveguidetip 108 along one or more axes orthogonal to axis 150, such that thewaveguide tip 108 scans a particular predefined pattern.

The intensity of light emitted by the radiation sources 102 a-c ismodulated so that the light is coupled into the waveguide 106 as asequence of pulses. The FSD device 100 coordinates the pulse sequencewith the actuation of the waveguide tip 108 such that light isselectively emitted from the waveguide tip 108 in a spatially-dependentmanner so as to form an image. For example, as the actuator 114 iscontinuously scanning the waveguide tip 108 according to a predictablepredefined pattern, the radiation sources 102 a-c each can selectivelyemit light and/or regulate the intensity of light emission according tothat pattern and in sufficiently short time intervals, such that thesequentially formed light pattern on the image plane 112 appears as animage to the user. This can be useful, for example, to depict objects,shapes, and/or patterns on the image plane 112. Further still, theradiation sources can also emit light in according to a dynamic pattern,such as a sequence of different images are projected onto the imagesource over time (e.g., to impart a sense of motion, such as in a videosequence, on the image plane 112).

As shown in FIG. 1A, the FSD device 100 includes a drive module 116 thatcoordinates the operation of the actuator 114 and the operation of theradiation sources 102 a-c. For instance, the drive module 116 cangenerate a drive signal to the actuator 114 to control the actuation ofthe actuator 114 (e.g., such that the actuator 114 causes the waveguidetip 108 to scan a predictable predefined pattern). The drive module 116can also generate a pixel modulation signal to regulate the output ofthe radiation sources 102 a-c in accordance with the actuation of theactuator 114. The drive signal and the pixel modulation signal can betransmitted simultaneously to the actuator 114, such that pixels areformed at specific spatial locations along the image plane 112.

As an example, a drive signal can be modulated in accordance with theexemplary pattern shown in plot 160 of FIG. 1C, such that the signalconstitutes a sinusoidal drive signal that is amplitude modulated overtime. The drive signal can include a sinusoidal signal portion thatdrives one scan axis of actuator 114, as well as a second sinusoidalsignal portion that drives a second scan axis. The second sinusoidaldrive signal is phase-shifted relative to the first drive signalportion, such that the waveguide tip 108 sweeps through a circular scanpattern. The sinusoidal drive signal can be amplitude modulated overtime to dilate and contract this circular scan pattern to form anarea-filling spiral scan pattern. A simplified scan pattern 170 is shownin FIG. 1D. Similarly, the pixel modulation signal can be generated inaccordance with the scan pattern 170, such that pixels are formed atspecific spatial locations along the scan pattern 170.

In some cases, multiple FSD devices can be used in conjunction (e.g., ina two-dimensional array) to increase the quality of the projected image.As an example, multiple FSD devices can be implemented in an array toincrease the resolution of projected images, increase the pixel densityof projected images, and/or to increase the frame rate by which imagesare projected.

Implementations of the FSD device 100 can be used in a variety ofimaging applications. For example, in some cases, FSD devices 100implemented in a head mounted display device. One or more FSD devices100 can be used to project images onto eyepieces positioned over auser's eyes, such that they are within the user's field of view. In somecases, FSD devices 100 can be implemented as a part of a “virtualreality” system or an “augmented reality” system to present images in avisually immersive manner.

As described with respect to FIG. 1A, an actuator 114 imparts a forceonto the waveguide 106, such that the waveguide tip 108 is scanned alongone or more axes according to a predictable predefined pattern. This canbe implemented by mechanically coupling the actuator 114 to thewaveguide 106 using a mechanical joint 200.

FIGS. 2A and 2B show a perspective view (FIG. 2A) and a cross-sectionalview (FIG. 2B) of an example actuator 114, an example waveguide 106, andan example mechanical joint 200. For ease of illustration, portions ofthe actuator 114 have been omitted. FIGS. 3A-3D show the mechanicaljoint 200 according to a front perspective view (FIG. 3A), a rearperspective view (FIG. 3B), a cross-sectional view (FIG. 3C), and a topview (FIG. 3D).

The actuator 114 extends along a longitudinal axis 150. The actuator 114has a tube-like configuration, and includes an outer wall 204 encirclinga hollow inner channel 206. The actuator 114 has a circular orsubstantially circular cross-section. In some cases, the actuator 114 isa piezoelectric tube actuator.

The waveguide 106 is threaded through the inner channel 206 of theactuator 114, and extends along the longitudinal axis 150. The waveguide106 is mechanically coupled to the actuator 114 via the mechanical joint200, such that a force induced by actuator 114 (e.g., due to vibrationsgenerated by the actuator 114 along its outer wall 204) is coupled tothe waveguide 106. The waveguide 106 can be an optical fiber (e.g., asingle mode optical fiber).

The mechanical joint 200 includes a neck portion 208, a collar portion210, and a flexural element portion 212. In some cases, the mechanicaljoint 200 can be implemented as an integral component. In some cases,the mechanical joint 200 can be constructed from two or more discretecomponents.

The neck portion 208 is configured to attach to waveguide 106, such thatthe mechanical joint and the waveguide 106 are mechanically coupled. Insome cases, the neck portion 208 can be mechanically and/or chemicallyattached to the waveguide 106. For example, the neck portion 208 can beattached to the waveguide 106 through metallization or diffusion. Asanother example, the neck portion 208 can be attached to the waveguide106 through the use of urethanes, epoxies, or nanoparticles.

The neck portion 208 extends along the longitudinal axis 150. The neckportion 208 has a tube-like configuration, and includes an outer wall214 encircling a hollow inner channel 216.

The inner channel 216 is dimensioned to receive the waveguide 106. Insome cases, the cross-sectional shape of the inner channel 216 can beidentical or substantially identical as that of the waveguide 106. Forexample, the if the cross-sectional shape of the waveguide 106 iscircular or substantially circular, the inner channel 216 also can behave a circular or substantially circular cross-section. In some cases,the diameter of the inner channel 216 can be substantially the same asthe diameter of the waveguide 106, such that the waveguide 106 securelycontacts an inner surface 218 of the outer wall 214 facing thelongitudinal axis 150 (e.g., through a friction fit).

In some cases, the neck portion 208 can include one or more slots alongthe outer wall 214. For example, as shown in FIGS. 3A-3C, the neckportion 208 can include several slots 220 that extend through the outerwall 214. Each slot 220 can each extend partially or entirely along theneck portion 208. The slots 220 can be beneficial, for example, infacilitating flexure of the mechanical joint 200. As shown in FIGS.3A-3C, the slots 220 can be evenly azimuthally spaced about thelongitudinal axis 150. Although four slots 220 are shown in FIGS. 2A and3A-3C, in practice, the neck portion 208 can include any number of slots(e.g., one, two, three, or more slots), or no slots at all.

The collar portion 210 is configured to mechanically couple to theactuator 114. The collar portion 210 extends along the longitudinal axis150. The collar portion 210 has a tube-like configuration, and includesan outer wall 222 encircling a hollow inner channel 224.

The inner channel 224 is dimensioned to receive the actuator 114. Insome cases, the cross-sectional shape of the inner channel 224 can beidentical or substantially identical as that of the actuator 114. Forexample, the if the cross-sectional shape of the actuator 114 iscircular or substantially circular, the inner channel 224 also can behave a circular or substantially circular cross-section. In some cases,the diameter of the inner channel 224 can be substantially the same asthe diameter of the actuator 114, such that the actuator 114 securelycontacts an inner surface 226 of the outer wall 222 facing thelongitudinal axis 150 (e.g., through a friction fit). In some cases, thediameter of the inner channel 224 can be larger than the diameter of theactuator 114, such that a gap region 228 is defined between the innersurface 226 of the outer wall 222 and the actuator 114.

In some cases, the collar portion 210 can include one or more slotsalong the outer wall 222. For example, as shown in FIGS. 2A and 3A-3C,the collar portion 210 can include several slots 230 that extend throughthe outer wall 222. Each slot 230 can each extend partially or entirelyalong the collar portion 210. The slots 230 can be beneficial, forexample, in facilitating flexure of the mechanical joint 200. Althoughfour slots 230 are shown in FIGS. 2A and 3A-3C, in practice, the collarportion 210 can include any number of slots (e.g., one, two, three, ormore slots), or no slots at all.

The flexural element portion 212 is configured to mechanically couplethe neck portion 208 to the collar portion 210, such that forcesimparted onto the collar portion 210 (e.g., due to vibrations generatedby the actuator 114) are coupled to the neck portion 208. In some cases,portions of flexural element portion 212 or an entirety of the flexuralelement portion 212 can bend with respect to the neck portion 208 and/orthe collar portion 210, such that the neck portion 208 and the collarportion 210 are not rigidly coupled together.

The flexural element portion 212 can include various structuresextending between the neck portion 208 and the collar portion 210. Forexample, as shown in FIGS. 2A-2D and 3A-3D, the flexural element portion212 can include an annular portion 232 (e.g., a flange or nm) and beam234 extending between and interconnecting the neck portion 208 and thecollar portion 210. Although four beams 234 are shown in FIGS. 2A, 3A,and 3D, in practice, the flexural element portion 212 can include anynumber of beam 234 (e.g., one, two, three, or more slots). In somecases, the flexural element portion 212 can have no beams at all, andthe annular portion 232 alone can extend along from the neck portion 208to the collar portion 210. Further still, in some cases, the flexuralelement portion 212 does not include an annular portion 232 at all(e.g., each of the beams 234 can extend from the neck portion 208directly to the collar portion 210). Other configurations also can beused to vary the stiffness of the flexural element portion 212.

In some cases, the mechanical joint 200 can be rotationally symmetricabout the longitudinal axis 150. In some cases, the mechanical joint 200can have at least four-fold rotational symmetry about the longitudinalaxis 150.

In some cases, the mechanical joint 200 can have directionally dependentstiffness. For example, referring to FIG. 3D, the mechanical joint 200can have a first translational stiffness k_(z) with respect to thelongitudinal axis 150 (i.e., the z-axis), a second translationalstiffness k_(x) with respect to the x-axis, and a third translationalstiffness k_(y) with respect to the y-axis (where the x, y, and z axesrefer to the axes of a Cartesian coordinate system). The firsttranslational stiffness k_(z) can be different than each of the secondtranslational stiffness k_(x) and the third translational stiffnessk_(y). For example, the first translational stiffness k_(z) can begreater than each of the second and third translational stiffnessesk_(x) and k_(y). Further, in some cases, the second translationalstiffness k_(x) and the third translational stiffness k_(y) can besubstantially the same.

Further, the mechanical joint 200 can have a first rotational stiffnessk_(θx) about the x-axis, a second rotational stiffness k_(θy) about they-axis. The first and second rotational stiffnesses k_(θx) and k_(θy)can be substantially the same, and each rotational stiffness can be lessthan the first translational stiffness k_(z).

This combination of stiffnesses can be useful, for example, as itenables the mechanical joint 200 to couple force from the actuator 114uniformly with respect to the x-y plane, such that the waveguide 106less likely to exhibit directionally-dependent bias with respect to thex-y plane during operation of the actuator 114. Thus, the waveguide 106is more likely to travel along a predictable predefined scan pattern,thereby improving the projected image quality. Further, as the firsttranslation stiffness k_(z) is relatively large, the waveguide 106 isless along to translate along the z-axis, while still enabling itvibrate with respect to the x and y axes.

Further still, in some cases, the stiffnesses can be modified to varythe behavior of the waveguide 106 (e.g., to increase or decrease thedeflection angle of the waveguide tip 108 during operation of theactuator 114 and/or to change the natural or resonant frequency of thewaveguide tip 108 during operation). Thus, the performance of the FSDdevice 100 can be adjusted by modifying the stiffnesses of themechanical joint 200. In some cases, the mechanical joint 200 enablesthe waveguide tip 108 to scan a pattern at a frequency of approximately10 kHz to 150 kHz and to achieve a diametral deflection between 600 μmand 1800 μm (e.g., the tip 108 of traverses a circular or substantiallycircular path having a diameter between 600 μm and 1800 μm). Otherperformance characteristics are also possible, depending on theimplementation.

As examples, in some cases, a typical radial translation stiffness canbe between 0.375 N/mm and 6.0 N/mm, with a buckling mode stiffnessbetween 1.7 N/mm and 28 N/mm. In some cases, a typical axial translationstiffness can be between 1.2 N/mm and 20.0 N/mm, with a buckling modestiffness between 20.0 N/mm and 360.0 N/mm. In some cases, a typicalrotational stiffness can be between 0.1 N*mm/Rad and 1.6 N*mm/Rad, witha buckling mode stiffness between 0.15 N*mm/Rad and 2.5 N*mm/Rad.

In some cases, each slot 220 can be radially aligned with acorresponding slot 230 and a corresponding beam 234. For example, asshown in FIGS. 4A and 4B, a first slot 220 a, a first slot 230 a, and afirst beam 234 a are each disposed at a first radial direction 402 awith respect to the longitudinal axis 150. Further, a second slot 220 b,a second slot 230 b, and a second beam 234 b are each disposed at asecond radial direction 402 b with respect to the longitudinal axis 150.Further, a third slot 220 c, a third slot 230 c, and a third beam 234 care each disposed at a third radial direction 402 c with respect to thelongitudinal axis 150. Further, a fourth slot 220 d, a fourth slot 230d, and a fourth beam 234 d are each disposed at a fourth radialdirection 402 d with respect to the longitudinal axis 150.

Further, the directions can be evenly azimuthally spaced around thelongitudinal axis 150. For example, as shown in FIGS. 4A and 4B, theradial directions 402 a-d are azimuthally spaced in 90° increments withrespect to the longitudinal axis 150. In some cases, the radialdirections 402 a-d can each align with a respective piezoelectricelement of the actuator 114. For instance, in the example shown in FIG.4C, the actuator 114 includes four lines of piezoelectric elements(e.g., piezo-ceramic elements) that are evenly azimuthally spaced aboutthe longitudinal axis 150, and electrode plates disposed betweenadjacent piezoelectric elements (due to the perspective view of FIG. 4C,only two piezoelectric elements 404 a and 404 b, and three electrodeplates 406 a-c are shown). As shown in FIG. 4C, the first radialdirection 402 a can be radially aligned with a first piezoelectricelement 404 a, and the second radial direction 402 b can be radiallyaligned with a second piezoelectric element 404 b. Similarly, the thirdradial direction 402 c and the fourth radial direction 402 d can each beradially aligned with a third piezoelectric element and a fourthpiezoelectric element, respectively.

This configuration can be useful, for example, to define the axes ofmotion of the FSD device 100 and/or to reduce directionally-dependentbias with respect to the x-y plane during operation of the actuator 114.

Although an example configuration of a mechanical joint 200 is shown inFIGS. 2A, 2B, 3A-3D, and 4A-4C, this is merely an illustrative example.In practice, the configuration of a mechanical joint can differ,depending on the application (e.g., to accommodate differently sizedactuators and/or waveguides, to provide different stiffness properties,to provide different waveguide deflection characteristics, etc.).

As an example, FIGS. 5A-5C show another mechanical joint 500. FIG. 5Ashows a perspective view of the mechanical joint 500, FIG. 5B shows atop view of the mechanical joint 500, and FIG. 5C shows across-sectional view of the mechanical joint 500 along the plane A.

The mechanical joint 500 is similar in some respects to the mechanicaljoint 200. For example, the mechanical joint 500 includes a neck portion502, a collar portion 504, and a flexural element portion 506. The neckportion 502 is configured to mechanically couple to a waveguide (e.g.,the waveguide 106) through a mechanical and/or chemical attachmentbetween them. Further, the collar portion 504 is configured tomechanically couple to an actuator (e.g., the actuator 114). Further,the flexural element portion 506 is configured to mechanically couplethe neck portion 502 to the collar portion 504, such that forcesimparted onto the collar portion 504 (e.g., due to vibrations generatedby an actuator) are coupled to the neck portion 502.

The flexural element portion 506 also includes an annular portion 508(e.g., a flange or nm) extending between and interconnecting the neckportion 502 and the collar portion 504. A number of slots can be definedon the annular portion 508. For example, as shown in FIGS. 5A-5C, threeslots 510 can be defined on the annular portion 508, each extendingspirally outward from the neck portion 502. The slots 510 can berotationally symmetrically defined about the longitudinal axis 512 ofthe mechanical joint 500 (e.g., each slot 510 can be rotationally offsetfrom an adjacent slot 510 by 1200). Although three slots 510 are shownin FIGS. 5A-5C, this is merely an illustrative example. In practice, amechanical joint can include any number of slots 510 (e.g., one, two,three, four, or more).

Further, as shown in FIG. 5B, the slots 510 are confined within anotional circle B. In practice, the size of the circle B can differ,such that the slots 510 occupy a greater or lesser area of the annularportion 508.

Further, as shown in FIGS. 5A and 5C, the mechanical joint 500 alsoincludes a hub step structure 514. The hub step structure 514 extendsoutward from the flexural element portion 506, and encircles the neckportion 502, forming a step or indentation 516. The hub step structure514 can be useful, for example, in providing additional stiffness to themechanical joint 500.

FIGS. 6A-6C show another example mechanical joint 600. FIG. 6A shows aperspective view of the mechanical joint 600, FIG. 6B shows a top viewof the mechanical joint 600, and FIG. 6C shows a cross-sectional view ofthe mechanical joint 600 along the plane A.

The mechanical joint 600 is similar in some respects to the mechanicaljoint 200. For example, the mechanical joint 600 includes a neck portion602, a collar portion 604, and a flexural element portion 606. The neckportion 602 is configured to mechanically couple to a waveguide (e.g.,the waveguide 106) through a mechanical and/or chemical attachmentbetween them. Further, the collar portion 604 is configured tomechanically couple to an actuator (e.g., the actuator 114). Further,the flexural element portion 606 is configured to mechanically couplethe neck portion 602 to the collar portion 604, such that forcesimparted onto the collar portion 604 (e.g., due to vibrations generatedby an actuator) are coupled to the neck portion 602.

The mechanical joint 600 also includes a hub step structure 610. The hubstep 610 structure includes several finger structures 612, eachextending outward from the flexural element portion 606. For example, asshown in FIGS. 6A and 6B, the mechanical joint 600 can include eightfinger structures 612 that protrude from the flexural element portion606 and encircle the neck portion 602. The finger structures 612 can berotationally symmetrically disposed about the longitudinal axis 608 ofthe mechanical joint 600 (e.g., each finger structure 612 can berotationally offset from an adjacent finger structure 612 by 45°).Although eight finger structures 612 shown in FIGS. 6A-6C, this ismerely an illustrative example. In practice, a mechanical joint caninclude any number of finger structures 612 (e.g., one, two, three,four, or more).

Further, the finger structure 612 form a step or indentation 614. In asimilar manner as described with respect to FIGS. 5A-5C, the hub stepstructure 610 can be useful, for example, in providing additionalstiffness to the mechanical joint 600.

FIGS. 7A-7C show another example mechanical joint 700. FIG. 7A shows aperspective view of the mechanical joint 700, FIG. 7B shows a top viewof the mechanical joint 700, and FIG. 7C shows a cross-sectional view ofthe mechanical joint 700 along the plane D.

The mechanical joint 700 includes a neck portion 702, a collar portion704, and a gimbal structure 706. The neck portion 702 is configured tomechanically couple to a waveguide (e.g., the waveguide 106) through amechanical and/or chemical attachment between them. Further, the collarportion 704 is configured to mechanically couple to an actuator (e.g.,the actuator 114).

Further, the gimbal structure 706 is configured to mechanically couplethe neck portion 702 to the collar portion 704, such that forcesimparted onto the collar portion 704 (e.g., due to vibrations generatedby an actuator) are coupled to the neck portion 702. The gimbalstructure 706 includes a ring 708, inner beams 710 mechanically couplingthe ring 708 to the neck portion 702, and outer beams 712 mechanicallycoupling the ring 708 to the collar portion 704.

As shown in FIG. 7B, the ring 708 is ovular in shape, and is centeredabout a longitudinal axis 714 of the mechanical joint 700. The innerbeams 710 extend inward from the inner periphery of the ring 708 alongthe major axis 716 of the ring 708. The outer beams 712 extend outwardfrom the outer periphery of the ring 708 along the mirror axis 718 ofthe ring 708. Further, the major axis 716 is orthogonal to the minoraxis 718. Thus, the inner beams 710 and the outer beams 712 arerotationally from one another by 90°.

The gimbal structure 706 enables the neck portion 702 to rotate withrespect to the collar portion 704 substantially about two discrete axesof rotation (e.g., about the major axis 716 and about the minor axis718). For example, as the ring 708 is mechanically coupled to the collarportion 704 through the outer beams 712, the ring 708 can rotaterelative to the collar portion 704 about minor axis 718. This rotation,in turn, similarly rotates the neck portion 702 relative to the collarportion 704 about the minor axis 718. Further, as the ring 708 ismechanically coupled to the neck portion 702 through the inner beams710, the neck portion 702 can rotate relative to the ring 708 about themajor axis 716.

This arrangement confines the movement of the neck portion 702 relativeto the collar portion 704 along a discrete number of rotational axes.This can be useful, for example, in improving the operationalcharacteristics of the mechanical joint (e.g., by eliminating orotherwise reducing errant movement along other axes of rotation).

Although example mechanical joints are depicted herein, it is understoodthat they are not necessarily drawn to scale. In practice, thedimensions of each structure of a mechanical joint can vary, depend onthe application. As examples, various dimensions of a mechanical jointare described below. However, it is understood that, in practice, otherdimensions are also possible.

In some cases, an inner diameter of a collar portion can be between 500μm and 1500 μm (e.g., 502 μm, 612 μm, 804 μm, 940 μm, or 1242 μm). Insome cases, an outer diameter of a collar portion can be between 800 μmand 2000 μm (e.g., 802 μm, 912 μm 802 μm, 912 μm, 1104 μm, 1214 μm, 1240μm, and 1542 μm). In some cases, an inner diameter of a neck portion canbe between 20 μm and 200 μm (e.g., 26 μm, 72 μm, 82 μm, 84 μm, 102 μm,127 μm, 129 μm, 140 μm, 185 μm, 204 μm, 260 μm, and 556 μm). In somecases, an outer diameter of a neck portion can be 300 μm or less (e.g.,300 μm, 150 μm, 100 μm, and 50 μm). In some cases, an inner diameter ofa hub step structure can be between 50 μm and 1000 μm (e.g., 84 μm, 127μm, 129 μm, 130 μm, 160 μm, 185 μm, 190 μm, 204 μm, 260 μm, and 556 μm).In some cases, a diametrical thickness of a hub step structure can bebetween 10 μm and 60 μm (e.g., 20 μm and 50 μm). In some cases, athickness of a flexural element portion can be between 20 μm and 60 μm(e.g., 30 μm and 50 μm).

In some cases, a thickness of an inner beam of a gimbal structure (e.g.,in a direction orthogonal to the longitudinal axis of the mechanicaljoint) can be between 5 μm and 50 μm (e.g., 10 μm and 15 μm). In somecases, a thickness of an outer beam of a gimbal structure (e.g., in adirection orthogonal to the longitudinal axis of the mechanical joint)can be between 5 μm and 50 μm (e.g., 11 μm and 17 μm). In some cases,the length of an outer beam of a gimbal structure (e.g., in anotherdirection orthogonal to the longitudinal axis of the mechanical joint)can be between 50 μm and 150 μm (e.g., 100 μm and 125 μm).

In some cases, a thickness of a spirally extending slot defined along aflexural element portion can be between 10 μm and 100 μm (e.g., 18 μm,21 μm, 22 μm, 26 μm, 28 μm, 32 μm, 35 μm, 72 μm, 78 μm, 81 μm). In somecases, spirally extending slots can be parametrically defined by theequations: x(t)=(A₁+B₁*T*π/180)*(cos(T*π/180)/1000 andy(t)=(A₁+B₁*T*π/180)*(sin(T*π/180)/1000, where 0≤T≤θ_(f). A₁ can bebetween 100 μm and 200 μm (e.g., 102 μm, 108 μm, 111 μm, 124 μm, 125 μm,129 μm, 135 μm, 175 μm, 181 μm). B₁ can be between 10 μm and 100 μm(e.g., 23 μm, 24 μm, 25 μm, 28 μm, 30 μm, 31 μm, 32 μm, 52 μm, and 53μm). θ_(f) can be between 200 and 350° (e.g., 220°, 262°, 272°, 277°,278°, 279°, 296°, 299°, 301°, 304°, 315°).

Further, although various structures are depicted herein, it isunderstood that various features can be combined onto a singlemechanical joint, and/or excluded from a mechanical joint. As anexample, a mechanical joint can include one or more of spirallyextending slots defined on a flexural element portion (e.g., as shown inFIGS. 5A-5C), a hub step structure (e.g., as shown in FIGS. 5A-5C and6A-6C), a hub step structure having finger structures (e.g., as shown inFIGS. 6A-6C), a gimbal structure (e.g., as shown in FIGS. 7A-7C), slotsdefined on a collar portion (e.g., as shown in FIG. 3B), slots definedon a neck portion (e.g., as shown in FIG. 3B), or any combinationthereof.

A mechanical joint can be constructed using various materials. Forexample, in some cases, the mechanical joint can be constructed, eitherpartially or entirely, of silicon. In some cases, the mechanical jointcan be constructed using a crystalline silicon (e.g., silicon having a(111) crystal structure) and/or an amorphous silicon. In some cases, themechanical joint can be constructed using one or more layers of siliconand/or one or more layers of an electrically insulative material (e.g.,silicon dioxide).

In some cases, a mechanical joint can be constructed using semiconductormicrofabrication techniques. A simplified example is shown in FIGS.8A-8C.

As an example, FIG. 8A shows a cross-sectional view of a wafer 800. Thewafer 800 includes a device layer 810 (e.g., a layer of silicon), aburied oxide layer 820 (e.g., a layer of silicon dioxide), and a handlelayer 830 (e.g., a layer of silicon). These layers can be formed, forexample, by depositing each of the layers in succession onto a substrate(e.g., using oxidation, physical vapor deposition, chemical vapordeposition, electroplating, spin casting, or other layer depositiontechniques).

One or more features can be defined on the wafer 800 by selectivelyadding and/or removing material from the wafer 800. For example, asshown in FIG. 8B, material can be etched from the wafer 800 to definechannels 840.

Material from the wafer 800 can be added and/or removed in such a waythat the remaining material forms the mechanical joint. For example, asshown in FIG. 8C, material can be selectively removed along theperiphery of the wafer 800, such that a substantially cylindricalportion of the wafer 800 remains, forming the outer periphery of theouter wall 222 of the collar portion 210 of the mechanical joint 200.Further, material can be selectively removed along the interior of thewafer 800 to define the inner channels 216 and 224. In a similar manner,additional material can be removed from the wafer 800 to define each ofthe other structures of the mechanical joint 200. As an example, wafer800 can be etched using photolithography techniques (e.g., wet etchingor dry etching, such as reactive-ion-etching and deep-reactive-ionetching).

Producing a mechanical joint using microfabrication techniques canprovide various benefits. For example, in some cases, mechanical jointscan be constructed precisely and consistently, and thus may be suitablefor use in variation-specific applications (e.g., in imaging systemsthat may be highly sensitive to the properties of a mechanical joint,such as FSD devices). Further, mechanical joints can be readily massproduced. Further still, the design of mechanical joints can be readilymodified and implemented, and thus can be readily used in a variety ofdifferent applications.

Although an example microfabrication process is shown FIGS. 8A-8C, thisis merely a simplified example. In practice, other microfabricationtechniques can be used to product a mechanical joint and/or to producemechanical joints having different structural features that those shownherein. For example, similar techniques can also be used to form anyother mechanical joint described herein (e.g., the mechanical joints500, 600, and 700).

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the invention. Accordingly, other embodimentsare within the scope of the following claims.

What is claimed is:
 1. A method comprising: directing light from a lightsource into an optical fiber, the optical fiber being threaded throughan aperture of a neck of a mechanical joint, the mechanical joint beingmechanically attached to an actuator along an inner surface of a collarof the mechanical joint, the neck and the collar being mechanicallycoupled via a flexural element extending from the neck to the collar;and operating the actuator to vary an orientation of a first end of theoptical fiber extending from the mechanical joint according to a spiralpattern.
 2. The method of claim 1, further comprising: emitting thelight from the first end of the optical fiber towards a subject.
 3. Themethod of claim 1, wherein the subject is a user's eye.
 4. The method ofclaim 1, further comprising: generating a light modulation signal and adrive signal; generating, using the light source, the light according toa light modulation signal; and operating the actuator according to thedrive signal.
 5. The method of claim 4, wherein the light modulationsignal regulates an output of the light source in accordance with thespiral pattern.
 6. The method of claim 5, wherein the drive signalregulates an operation of the actuator to vary the orientation of thefirst end of the optical fiber according to the spiral pattern.
 7. Themethod of claim 5, further comprising emitting the light from the firstend of the optical fiber to form an image on an image plane.
 8. Themethod of claim 1, wherein operating the actuator comprises coupling amechanical force generated by the actuator to the optical fiber usingthe mechanical joint.
 9. The method of claim 8, wherein the flexuralelement of the mechanical joint comprises one or more beams extendingbetween the neck and the collar, and wherein the mechanical forcegenerated by actuator is coupled to optical fiber, at least in part,through the one or more beams.
 10. The method of claim 8, wherein theflexural element of the mechanical joint comprises a gimbal structure,and wherein the mechanical force generated by actuator is coupled tooptical fiber, at least in part, through the gimbal structure.
 11. Theapparatus of claim 1, wherein the flexural element defines one or moreslots extending through the flexural element, the one or more slotsbeing spirally arranged about the axis.
 12. The apparatus of claim 1,wherein the flexural element comprises a gimbal structure.
 13. Anapparatus, comprising: an optical fiber; an actuator configured togenerate a force to vary an orientation of a first end of the opticalfiber according to a spiral pattern; and a joint mechanically couplingthe actuator to the optical fiber, wherein the joint is configured tocouple the force generated by the actuator to the optical fiber, andwherein the joint comprises: a neck extending along an axis, the opticalfiber being threaded through an aperture extending along the axisthrough the neck, wherein the optical fiber is attached to the joint ata surface of the neck facing the axis, a collar extending along theaxis, wherein the actuator is mechanically attached to the joint at aninner surface of the collar facing the axis, and a flexural elementextending radially from the neck to the collar.
 14. The apparatus ofclaim 13, wherein the optical fiber is configured to emit the light fromthe first end of the optical fiber towards a subject.
 15. The apparatusof claim 13, wherein the subject is a user's eye.
 16. The apparatus ofclaim 13, further comprising: a drive module configured to generate alight modulation signal; and a light source configured to generate lightaccording to the light modulation signal and provide the light to asecond end of the optical fiber opposite the first end, wherein thelight modulation signal regulates an output of the light source inaccordance with the spiral pattern.
 17. The apparatus of claim 16,wherein the drive module is configured to generate a drive signal,wherein the drive signal regulates an operation of the actuator to varythe orientation of the first end of the optical fiber according to thespiral pattern.
 18. The apparatus of claim 17, wherein the apparatuscomprises a head mounted display device.
 19. The apparatus of claim 13,wherein the actuator comprises a plurality of piezoelectric elementsazimuthally spaced about the axis.
 20. The apparatus of claim 19,wherein the plurality of piezoelectric elements are azimuthally spacedequally about the axis.
 21. The apparatus of claim 19, wherein theplurality of piezoelectric elements are azimuthally spaced 90° about theaxis.
 22. The apparatus of claim 13, wherein the flexural elementcomprises one or more beams extending between the neck and the collar.23. The apparatus of claim 13, wherein the joint has a first stiffnesswith respect to the axis, a second stiffness with respect to a firstradial direction, and a third stiffness with respect to a second radialdirection orthogonal the first radial direction, and wherein the firststiffness is greater than the second stiffness and the third stiffness.24. The apparatus of claim 13, wherein the joint comprises crystallinesilicon.
 25. The apparatus of claim 13, wherein the joint comprisesamorphous silicon.
 26. The apparatus of claim 13, wherein the jointcomprises one or more layers of silicon and one or more layers ofelectrically insulative material.
 27. The apparatus of claim 13, whereinthe neck defines one or more slots along a periphery of the neck.